Butene and butadiene purification by plural stage distillation



United States Patent Office ,849 Patented eh. I,

3,232,849 BUTENE AND BUTADIENE PURIFHCATIWQ BY PLURAL STAGE DISTHLLATIONGraham A. Renherg, llartlesville, kla., assignor to Phillips PetroleumCompany, a corporation of Delaware Filed Oct. 27, 1961, Ser. No. 148,1888 Claims. (Cl. 2il3--51) This invention relates to a method andapparatus for the separation and recovery of butadiene and of butenesfrom products resulting from the catalytic dehydrogenation of butenesand of n-butane, respectively, by a combination of fractional andextractive distillation steps.

In a commercial process for the manufacture of butadiene, including thefollowing steps: (1) butane dehydrogenation to butenes, (2) butenesrecovery or purification, (3) butenes dehydrogenation to butadiene, and(4) butadiene recovery or purification, the use of furfural as aselective solvent in the extractive distillation of butenes andbutadiene has made the process practical and economical. The use offurfural permits separations of C hydrocarbons which were heretoforeconsidered impossible or impractical on a commercial scale. It was thistype of separation upon which the production of the high puritybutadiene depended. Furfural absorbers were used to separate normalbutane from unsaturated C, hydrocarbons (step 2) and also for separatingbutadiene from butenes in the butadiene purification or recovery step(step 4). are of conventional bubble cap type and in the preferredmodification are constructed in a pair of SO-tray sections. The functionof the absorbers is to separate the product of that step from therecycle material (to the preceding step) while the remainder of thecolumns (fractionator) function on the whole as auxiliary columns toincrease absorber feed purity or to process by-product streams. Sincebutenes in the normal butane recycle to the step 1) dehydrogenation andbutadiene in the butenes recycle to step (3) dehydrogenation arepartially destroyed over the catalysts, substantial losses are sufferedwhen upset or inferior operation of the absorbers occurs leaving largerthan normal amounts of butenes and butadiene in the recycle streams. Inaddition, normal butane in the kettle product takes a free ride throughthe butene dehydrogenation step acting as a diluent. Also, butenes inthe kettle product of step (4) absorbers unnecessarily overload thebutadiene purification column downstream of the absorber.

Prior art ordinarily employs indirect heat exchange With steam or with ahot plant product to provide reboiling heat to fractional distillationcolumns. To improve stripping in such operations, open steam isfrequently employed where Water resulting from steam condensation is notobjectionable.

The terms extractive distillation towers, columns or absorber are usedinterchangeably herein.

An object of this invention is to provide a method and apparatus for therecovery of butenes and of butadiene from separate process streamscontaining these materials. It is a further object of this invention toprovide an improved process and apparatus for the recovery of butadienesand of butenes involving extractive distillations. It is a furtherobject of this invention to provide apparatus in such a process in whichsubstantial energy savings are effected over conventional operations forthe recovery of these materials.

In the drawing, FIGURE 1 illustrates, in diagrammatic form, anarrangement of apparatus parts for carrying out an embodiment of thisinvention.

FIGURE 2 illustrates, in diagrammatic for-m, another These absorbercolumns arrangement of apparatus parts for carrying out an alternativeprocess embodiment of this invention.

The method of manufacturing butadiene by the two stage dehydrogenationof butane is well known. One of the major costs of this method for theproduction of butadiene is in the energy requiremehts demanded by thepurification steps.- These process steps involve essentially a series offractionation and extractive distillation steps.

In one typical process the purification train comprises essentially twofractional distillation columns and two extractive distillation columns.The first of the fractional distillation columns serves primarily toseparate butene-1 from butene-2 produced in the dehydrogenation ofnormal butane. The distillation column effecting this separation isherein termed thebutene-l column. The bottoms from the butene-l columncomprising essentiaily n-butane (normal butane) and butene-2 is passedto a butene absorber which absorbs the major portion of the butenestherefrom. Normal butane is rejected as an overhead stream and isrecycled to the original dehydrogenation step. This riormal butanereject stream .is produced as an overhead stream from the buteneabsorber (butene extractive distillation column). Overhead vapors fromthe butene-1 fractionator comprising essentially butene-1 and the smallamount of butadiene are combined with overhead vapors from a butene-2column, said overhead vapors from said butene2 e61 umn comprisingessentially butene-1 and butadiene. The" butene-1 column distills then-butane dehydrogenation effluent as feed stock and passes butene-1overhead'fro'm the column while the butene-2 column distills" thebutenes dehydrogenation efiluent and separates material rower boilingthan butene-2 as overhead and concentrates thef butene-2 in the kettleproduct. The feed to the butene-2 column is a deoiled and depropanizedstream comprising essentially butadiene and normal butenes produced inthe" second stage dehydrogenation. The combined overhead vapors from thebutene-1 column and from the butene-2 column are then passed to abutadiene absorber or extractive distillation column in which butadieneis absorbed in a selective solvent.

I have now found that purification energy requirements can besubstantially reduced by using rich solvent or' absorbent from thebutene absorber, without stripping, as a solvent feed to the butadieneabsorber. found that a portion of the overhead vapors from the butadiene absorber can be effectively used as reboil or boil-up material inthe butene absorber with the result that energy requirements in thebutene absorber are markedly reduced. The butadiene rich absorbent fromthe kettle section of the butadiene absorber is stripped of its mean enecontent in a stripping column. I have also found that a portion of thevapors produced in this stripping column can be used to reboil orboil-up the kettle seetion of the butadiene absorber with the resultthat" further saving in heat requirements is obtained.

Use of boil-up vapors from subsequent columns for reboiling extractivedistillation columns upstream from the respective columns producing theoverheadvapors eliminates the need for the provision of conventionalreboilers in the extractive distillation columns.

Furthermore, in addition to the above-mentioned energy savings, I havealso found that one of the fractiona'tors in the recovery system can beeliminated in some instances.

Referring to the drawing and specifically to FIGURE 1, reference numeral11 identifies a conduit which passes the hydrocarbon stream produced indehydrogenation of normal butane, which stream has been deoiled for theremoval of high-boiling constituents therefrom, into a fractionaldistillation column A. Reference numeral 13 I have also identifies aconduit through which a hydrocarbon stream produced in the catalyticdehydrogenation of butenes and having been freed from propane and lowerboiling materials is passed to a fractional distillation column C. A

Also shown in FIGURE 1 of the drawing are considerable operating data,such as pressures, temperatures, and many heat quantities in terms ofB.t.u. per hour. By using the hot stripper bottoms at about 375 F. forpreconduit 13 passes overhead product from column A into 5 heating thefeed to this stripper considerable heat is also a conduit 22 into whichis also passed an overhead prodsaved. Heat exchanger 31 heats the chargeto the stripper not from column C by way of a conduit These com- E fromabout 170 F. to about 24% F. with the simulbined streams are passed onthrough a conduit 22 into taneous cooling of the lean furfural from"about 375 F. an extractive distillation column or absorber D. The toabout 180 F. Further cooling of this partially cooled distillationbottoms from column A is passed through a lean furfural is carried outin heat exchanger 32 with the conduit 14 into a column B herein calledthe butene abresult that the lean furfural is finally cooled to atemperasorber. A solvent, such as furfural, is passed through a ture ofabout 117 F. Overhead material downstream of conduit 30 into the upperportion of column B. Reboil the reflux condenser of column C has atemperature of or boil-up vapors are introduced into this column throughabout 120 F. a conduit 24 and extraction solvent, rich in dissolved ma-In Table I is given a material balance in terms of moles terial, ispassed through a bottoms outlet conduit 17 for per hour of variousconstituents in various process conpassage as the selective solvent intothe upper portion of duits. In both embodiments, i.e., FIGURES 1 and 2,the butadiene absorber D. Overhead product from colfurfural is employedas the extraction solvent.

TABLE I Material balance, 11 13 14 1s 17 24 1s 20 22 21 26 2s 29 30mols/hr.

Butane-1 256 253 3 3 1,626 1, 626 612 Butadiene 83 a 20 20 412 n-Butane9 1,524 1,513 53 42 1O t-Butene-2. 1 261 14 727 480 545 495 545 umn B iswithdrawn therefrom and is passed through In FIGURE 2 of the drawing isthe embodiment of the a conduit 16 for return to the original normalbutane invention in which the butene-2 column correspondingdehydrogenation step, not shown. Obviously, butene abto column C ofFIGURE 1 is not required. sorber B is operated under suitable extractivedistillation In FIGURE 2, conduit 51 transfers first stagedehydroconditions for the absorption of butene from the feed to genationeffluent, which has been deoiled, to a butene-1 the column with therejection of the normal butane for distillation column F. In this columnbutene-1 containrecycle purposes. The butene-rich solvent as mentioneding a very small proportion of butadiene is taken overis passed throughconduit 17 to the upper portion of the head and passed through a conduit52 to a subsequent butadiene absorber. The butene-rich stream flowingstep. Bottoms or kettle material from column F subthrough conduit 17contains a very small proportion of stantially freed of butene-l andbutadiene is passed butadiene. The stream flowing through conduit 22conthrough a conduit 53 as feed material to a butene abtains anappreciable portion of butadiene and this matesorber G. To this absorberis added lean solvent by way rial is considered the feed stock to theextractive distiilaof a conduit 57 from the source, subsequentlydescribed. tion column D. Upon operating this column under ex- Hotboil-up vapors are also added through a conduit 56 tractive distillationconditions an overhead vaporous prodwhile the solvent rich in butenesand containing a very" uct is produced containing butenes with a portionthereof minor portion of butadiene is passed through a conduit; beingpassed through a conduit 24 for boil-up purposes in 55 for use assolvent in a butadiene absorber H. Over the butene absorber. Excessoverhead material from head product normal butane is withdrawn fromcolumn column D is condensed and a portion of the condensate G andpassed to the first stage normal butane dehydrois returned to the columnas reflux while the remainder genation through a conduit 54. is passedthrough a conduit 25 for passage to the second Depropanized bottomsmaterial resulting from the secstage dehydrogenation, not shown, for theconversion 0nd stage dehydrogenation of butenes is passed through a ofbutenes to butadiene. conduit 58 and this stream is combined with theoverhead The bottoms material or solvent rich in butadiene is materialfrom still F flowing through conduit 52. This withdrawn from column Dthrough a conduit 26 containcombined stream passes on through a conduit59 and is ing a heat exchanger 31 and thence is passed into a stripintroduced into the butadiene absorber H as the feed ping column E. Inthis stripping column, butadiene is stock thereto. This column isoperated under butadiene stripped from the solvent and passed overheadfrom the extractive distillation conditions in which the butadiene iscolumn as hot vapors with a portion being passed through 0 absorbed bythe butene rich solvent introduced through a conduit 28 into the lowerportion of the butadiene abconduit 55. Hot overhead vapor from column His disorber D for boil-up purposes. The remainder of the vided into twoportions, one portion being passed throughoverhead material from columnE, not required for reconduit 56 for boil-up purposes in the buteneabsorber fluxing, is withdrawn through a conduit 29 and passed G, whilethe remainder, after being at least partially conto subsequentpurification steps, not shown. 5 densed, is passed through a conduit 60to the second stage: The bottoms material from stripper E is the leanabsorbor butene dehydrogenation step, not shown. The solvent,. cut andthis material is passed through a conduit 3%? rich in butadiene, asbottoms from the butadiene absorber through heat exchanger 31 and thencethrough. additional H is removed therefrom through a conduit 61 and thisheat exchange, if required, for introduction into the upper material isheated in exchanger 66 and then is introduced portion of the buteneabsorber B. 70 into a stripping still I for separation of butadiene. Hot

It should be pointed out that neither the butene abbutadiene-richoverhead vapors are divided into two porsorber B nor the butadieneabsorber D is provided with tions, one portion being passed through aconduit d2 for a reboiler system such as is ordinarily employed as ampleboil-up purposes in the butadiene absorber H while the reboiling andstripping are provided by use of the hot varemainder is condensed andpassed through a conduit 64 pOrs generated in the process. forsubsequent purification or other disposal, not Shown.

6 Open steam lines leading into columns D (FIG. 1) and H (FIG. 2)introduce steam to the lower section of these columns and water isremoved from columns E (FIG. 1) and J (FIG. 2) via the water lines inthe upper sections of these columns.

TABLE III Steam consumption in several pIOCess points FIGURES 1 and 2FURFURAL COLUMNS AND IIYDROOARBON FRACTIONATORS [Lb/hr. steam] Presentoperation Figure 1 Figure 2 p.s.i.g. 300 p.s.i.g. 30 p.s.i.g. 300p.s.i.g. 3O p.s.i.g. 300 p.s.i.g.

.Absorbers B, G 12, 000 207,000 17, 400 17, 400

Strippers tron Additional steam to butadiene column Total steam Total,MM.B.t.u./hr

is cooled in an exchanger 67, if desired, and passed on through aconduit '63 for addition into the top of the butadiene absorber H. Thisadditional solvent added to the top of butadiene absorber H is requiredin this embodiment because of the elimination of the conventionalbutene-2 distillation column.

The embodiment of FIGURE 2 employs a butene-rich overhead vaporousstream fromabsorber H for boil-up purposes in the butene absorber and abutadiene-rich overhead vaporous streamfrom the stripping still I forboil-up purposes in the butadiene absorber H. Also, the butadiene-richsolvent from the butene absorber is passed directly and withoutstripping as the solvent for use in the butadiene absorber H.

In FIGURE 2, the temperature of the overhead streams downstream of thereflux condensers of columns F, G, H, and! isabout 120 F. in each case.

In this specification and claims the butenes-rich solvent flowingthrough conduit 55 is sometimes termed an extract phase. Also thebutadiene-rich solvent flowing through conduit 61 is also sometimescalled an extract phase. The corresponding streams flowing throughconduits 17 and 26 in FIGURE 1 are also called extract phases.

In Table II is given a material balance of the components in the streamsin process in the operation illustrated in FIGURE 2 in terms of molesper hour. As mentioned hereinabove, one of the main points or advantagesof this invention is in the saving in cost of stripping steam by the useof the hot overhead vapors from several of the absorber and strippingcolumns.

The first double column in Table III illustrates the pounds of steam perhour required at the pressure of 30 p.s.i.g. (pounds per square inchgage) and at 300 p.s.i.g. In the second and third double columns aregiven the steam requirements at the two above-mentioned pressuresaccording to operation of FIGURE 1 and the operation of FIGURE 2. At aline immediately below the steam totals in these several columns aregiven to total B.t.u. requirements per hour in terms of millions ofB.t.u. Thus, in the line immediately below the present operation doublecolumn is the number 545. This 545 means 545 million B.t.u. per hour.This steam saving in terms of millions of B.t.u. per hour was figured at75 percent boiler efliciency and at a cost of 18 per million B.t.u.Thus, With the present operation as a basis, advantages or disadvantagesare calculatedaccording to the operations illustrated in FIGURE 1 andFIGURE 2. Thus, based on 75 percent boiler efiiciency and at 18 permillion B.t.u. the operation as practiced according to the processillustrated in FIGURE 1 provides a saving of $147,000 per year over aconventional process. And accordingly, the operation as practiced in theapparatus illustrated in FIGURE 2 provides an annual saving of 185,000per year over the conventional process.

As a limited refinement to the operation as illustrated in FIGURE 2, ifit is desired to de-oil the feed material flowing through conduit 58, asmall distillation column assembly identified by reference numeral 63can be employed. In this case, the proper valves are closed and othersare opened for putting the still 68 on stream for TABLE II Materialbalance, 51 52 53 54 55 56 57 58 59 6O 61 62 (i3 64 65 mols/hr.

Butenefl 256 253 3 3 1, 089 1, 089 Butadiene h 6 n-Butaue. 27 t-Butens-2 752 e-Butene-Z 789 Furiural.

Total 2, 396 346 2, 050 1, 530 19, 983 2, 663

In Table III is given process steam consumption at various processpoints in FIGURES 1 and 2 and also the saving in terms of dollar valuebased on fuel cost of 18 cents per million B.t.u.

moved from de-oiling the material flowing from conduit 58 prior to itsaddition to the material flowing from conduit 52 to conduit 59. In thiscase high boiling materials are rethe charge material entering thebutadiene absorber and such high boiling ends are thus not added to thesolvent for cycling around the operation.

As mentioned hereinabove, furfural is generally used as a solvent forthe extraction of butenes and for extraction of butadiene in bothembodiments disclosed herein. In absorbers B and G the reflux ratiosemployed were 0.5 to l, and in absorbers D and H the reflux ratios usedwere 0.65 to 1 under the temperature and pressure conditions given.

While furfural has been disclosed herein as the solvent used in columns,B, D and E of FIGURE 1 and in col umns, G, H and I of FIGURE 2, furfuralcontaining a small percentage of water is usually used in these columns.

The furfural to feed volume ratios in the butene absorbers B and G are 6to 1. The furfural to feed volum ratio in the butadiene absorber H is 10to 1.

While certain embodiments of the invention have been described forillustrative purposes, the invention obviously is not limited thereto.

I claim:

1. A method for the separation and recovery of butenes and butadienefrom a feed stream comprising butene-l, butadiene and n-butanecomprising extractively distilling said feed stream in the presence ofan extractant comprising furfural, butene-l, n-butane, trans-butene-Zand cis-butene-Z thereby producing an overhead product comprisingbutene-l, n-butane, trans-butene-Z and cis-butene-2 as one product ofthe operation and a bottoms product comprising furfural and butadienewith minor proportions of butene-l and butenes-2, distilling saidbottoms product at a substantially higher temperature than that in theaforesaid distilling thereby producing a butadiene rich vaporousoverhead product at said temperature, dividing this latter product intotwo portions, passing one portion into the extractive distillationoperation as boil-up medium and removing the other portion as anotherproduct, this latter distilling step producing a bottoms productcomprising furfural.

2. A method for separation and recovery of butadiene from a first and asecond feed stock each feed stock comprising in different proportionsbutene-l, butadiene, nbu-tane, t-butene-2 and c-butene-Z comprisingdistilling said first feed stock thereby producing a first overheadproduct containing predominantly butene-l and butadiene and a minoramount of n-butane and a first bottoms product containing predominantlyn-butane, t-butene-Z and c-butene-Z, extractively distilling said firstbottoms product in the presence of furfural and thereby rejectingn-butane and producing a first extract comprising furfural and the abovementioned butenes, combining the second feed stock with said firstoverhead product and extractively distilling the combined materials inthe presence of said first extract at a substantially higher temperaturethan that in the first mentioned distilling operation thereby producingan overhead stream comprising the above mentioned butenes and a secondextract comprising furfural and butadiene, dividing this lattermentioned overhead stream into two portions, passing one portion intothe first mentioned extractive distilling step as boil-up medium,distilling butadiene from said second extract at a substantially highertemperature than that in the second mentioned distilling operationthereby producing a bottoms product comprising furfural and an overheadbutadiene stream, dividing this butadiene stream into two portions,adding one portion to the second extractive distilling operation asboil-up medium and removing the other portion as a product, andreturning this latter furfural bottoms product to the first mentionedextractive distillation step as extractant.

3. A method for the separation and recovery of butadiene from a firstfeed stream comprising butene-l, butadiene and n-butane and produced inthe dehydrogenation of n-butane and a second feed stream comprisingbutene-l, butadiene, trans-butene-Z and cis-butene-2 produced in thedehydrogenation of butenes comprising combining these feed streams andextractively distilling the combined stream in the presence of furfuralcontaining butene-l, butenes-2 thereby producing a vaporous overheadproduct of butene-l and butenes-2 and a bottoms product of furfural andbutadiene and containing a minor proportion of butenes, distilling thislatter bottoms product at a substantially higher temperature than thatin the aforesaid extractive distilling operation into a butadiene-richvaporous overhead product and a furfural-rich bottoms product, dividingthe butadiene-rich vaporous overhead product into two portions, passingone portion at said higher temperature into the extractive distillationstep as boil-up medium, and condensing the other portion as product.

4. A method for the separation and recovery of butadiene from a firstfeed stream comprising n-butane, cis and trans butenes-2, and a secondfeed stream comprising butene-l, n-butane and butadiene produced in thecatalytic dehydrogenation of n-butane, and a third feed streamcomprising butadiene and butene-l with minor amounts of n-butane, cisbutene-Z and trans butene-Z, produced in the catalytic dehydrogenationof butenes comprising the step of extractively distilling said firstfeed stream in the presence of extractant furfural and a first boil-uphot vapor stream comprising butene-l, cis and trans butenes-2subsequently produced, and thereby producing a butane-rich overheadstream and a bottoms extract comprising furfural-rich butenes,extractively distilling said second and third feed streams in thepresence of said bottoms extract and a second boil-up hot vapor streamcomprising butadiene with minor proportions of butenes as subsequentlyproduced, this latter extractive distilling operation producing a firsthot vaporous overhead product comprising butenes and a bottoms productcomprising furfural rich in butadiene and containing a minor amount ofbutenes, stripping butadiene and butenes from this latter bottomsproduct thereby producing a second hot vaporous overhead productcomprising butadiene containing a minor proportion of butenes, dividingeach of said first and second hot vaporous overhead product into twoportions, returning one portion of said first overhead product to thefirst extractive distillation step as said first boil-up material, andreturning one portion of said second overhead product to the secondextractive distillation step as said second boil-up material, theremaining portions of the first and second overhead products beingproducts of the operation.

5. A method for the separation and recovery of butenes and butadienefrom a first feed stream produced in the catalytic dehydrogenation ofn-butane and a second feed stream produced in the catalyticdehydrogenation of hutene-l and butenes-2, said feed streams comprisingnbutane, butene-l, butadiene, trans butene-2 and cis butene-2,comprising the steps of distilling said first feed stream therebyproducing a first overhead product comprising butene-l with minoramounts of butadiene and n-butane and a first bottoms product comprisingn-butane with minor amounts of trans butene-2 and cis butene-2,distilling said second feed stream thereby producing a second overheadproduct comprising butene-l and butadiene and a second bottoms productcomprising cis and trans butenes-2, extractively distilling said firstbottoms product in the presence of furfural and a first hot vaporousboil-up material subsequently produced thereby producing a thirdoverhead product comprising n-butane and a first extract phasecomprising butene-l, cis and trans butenes-2 with minor amounts ofn-butane and butadiene, extractively distilling said first and secondoverhead products in the presence of said first extract phase and asecond hot vaporous boil-up material subsequently produced therebyproducing a fourth hot vaporous overhead product comprising butene-l andcis and trans butenes-2 with minor amounts of n-butane and butadiene anda second extract phase comprising butadiene and furfural with minoramounts of butene-l and cis and trans butenes-2, stripping said secondextract phase thereby producing a fifth hot vaporous overhead productcomprising butadiene containing minor amounts of butene-l and cis andtrans butenes-Z and a third bottoms product of furfural, returning thisfurfural as the furfural in the first mentioned extractive distilation,dividing the fourth hot v'aporous overhead product into two portions,one portion being the first hot vaporous boil-up material and the otherportion being a butenes product, and dividing the fifth hot vaporousoverhead into two portions, one portion being the second hot vaporousboil-up material and the other portion being a butadiene product of theoperation.

6. An apparatus comprising, in operable combination, first, second,third, fourth and fifth distillation columns said second and fourthcolumns being free of indirect reboiler means; first and second conduitscommunicating the overhead product outlet portions of the first andthird columns, respectively, with said fourth column at its feed level;a third conduit communicating the kettle section of said first columnwith said second column at its feed level; fourth, fifth and sixthconduits leading from the overhead product outlet portions of saidsecond, fourth and fifth columns, respectively; seventh, eighth andninth conduits communicating the kettle sections of said second, fourthand fifth columns with the vapor outlet portion of said fourth column,the feed level of said fifth column and the vapor outlet portion of saidsecond column, respectively; tenth and eleventh conduits com municatingthe fifth and sixth conduits with the kettle sections of said second andfourth columns, respectively to provide direct reboil for same and anoutlet for water from a level above said feed level of said fifthcolumn.

7. An apparatus comprising, in operable combination, first, second,third and fourth distillation columns; first, second, third and fourthconduits leading from the overhead product outlet portions of saidfirst, second, third and fourth columns respectively, said first conduitcommunicating with said third column at its feed level and also With asource of feed stock; fifth, sixth, seventh and eighth conduitscommunicating the kettle sections of said first, second, third andfourth columns with the second column at its feed level, the thirdcolumn at its overhead vapor outlet portion, the fourth column at itsfeed level, and the second column at its overhead vapor outlet portionrespectively; a ninth conduit also communicating the kettle section ofsaid fourth column with the overhead vapor outlet portion of said thirdcolumn, tenth and eleventh conduits communicating said third and fourthconduits respectively, with the kettle sections of said second and thirdcolumns respectively; and an outlet for Water from a level above thefeed level of said fourth column.

8. In the method of claim 5, dividing said third bottoms product offurfural into two portions, returning one portion as the furfural in thefirst mentioned extractive distilling and the other portion to thesecond extractive distilling as additional extraction solvent.

References Cited by the Examiner UNITED STATES PATENTS 2,379,332 6/1945Arnold 260-681.5 2,395,016 2/1946 Schulze et a1. 260681.5 2,619,81412/1952 Kniel 202- X 2,750,435 6/1956 Fetchin 20239.5 X 3,004,08310/1961 Siedenstrang et al. 202--39.5 X 3,059,037 10/1962 Cahn 202-395 XFOREIGN PATENTS 776,154 6/1957 Great Britain.

NORMAN YUDKOFF, Primary Examiner.

ALPHONSO D. SULLIVAN, Examiner.

1. A METHOD FOR THE SEPARATION AND RECOVERY OF BUTENES AND BUTADIENEFROM A FEED STREAM COMPRISING BUTENE-1, BUTADIENE AND N-BUTANECOMPRISING EXTRACTIVELY DISTILLING SAID FEED STREAM IN THE PRESENCE OFAN EXTRACTANT COMPRISING FURFURAL, BUTENE-1, TRANS-BUTENE-2 ANDCIS-BUTENE-2 THEREBY PRODUCING AN OVERHEAD PRODUCT COMPRISING BUTENE-1,N-BUTANE, TRANS-BUTENE-2 AND CIS-BUTENE-2 AS ONE PRODUCT OF THEOPERATION AND A BOTTOMS PRODUCT COMPRISING FURFURAL AND BUTADIENE WITHMINOR PROPORTIONS OF BUTENE-1 AND BUTENES-2, DISTILLING SAID BOTTOMSPRODUCT AT A SUBSTANTIALLY HIGHER TEMPERATURE THAN THAT IN THE AFORESAIDDISTILLING THEREBY PRODUCING A BUTADIENE RICH VAPOROUS OVERHEAD PRODUCTAT SAID TEMPERATURE, DIVIDING THIS LATTER PRODUCT INTO TWO PORTIONS,PASSING ONE PORTION INTO THE EXTRACTIVE DISTILLATION OPERATION ASBOIL-UP MEDIUM AND REMOVING THE OTHER PORTION AS ANOTHER PRODUCT, THISLATTER DISTILLING STEP PRODUCING A BOTTOMS PRODUCT COMPRISING FURFURAL.